In conventional machines for the precision working of the tooth flanks of toothed workpieces according to the mentioned method, a swivelling movement of the tool or the workpiece is coupled with a center distance change for producing a crown dimension. For example, in the gear shaving machine according to German OS No. 29 27 976 (corresponds to U.S. application Ser. No. 467,425, filed Feb. 17, 1983, which is a continuation of application Ser. No. 129,789, filed Mar. 12, 1980, now abandoned), a feed carriage which has the tool thereon is suspended tiltably about a transverse axis and is supported at one end through a guide bar in a rocker arm. If the guide bar is positioned horizontally, it slides in the rocker arm without influencing the feed carriage. If the guide bar, however, is inclined, the feed carriage tilts up and down during the back-and-forth feed movement, so that the shaving gear removes more material at the two opposite tooth ends of the workpiece than in the center, namely, crowned teeth are produced. The magnitude or size of the crown dimension can be changed simply by adjusting the angle of inclination of the guide bar. The extent of the crown dimension (convexity) is determined by the construction of the mentioned devices.
Deviations from the predetermined extent of the crown dimension are only possible with a differently formed, for example curved guide bar. The development and the manufacture of such curved guide bars, however, is very time consuming and thus expensive. A freely selectable crown dimension is in spite of this not achievable.
Therefore, the basic purpose of the invention is to provide a method and a machine which is suited therefor, with which it is possible to be able to choose in as free as possible a manner the size and form of the crown dimension.
In the inventive method, each point on the respective flank line has associated with it a specified center distance and a specified angle of traverse and a specified plunge angle, each of which is selected to correspond with the requirements, for example, of a desired form of the flank line. The tool follows then the desired form of the flank line, which must not only be formed convexly--as it was only possible up to now--but can also have straight and even concave sections. In order for the produced flank line to correspond as much as possible exactly with the desired one, the tool is always to be oriented so that the plane of rotation thereof extends perpendicularly with respect to the respective section of the flank line. For this reason, the axis for the swivelling movement of the rocking device extends at least approximately through the angle forming summit or midpoint of the center plane of rotation of the tool, which angle opens toward the workpiece.
With the suggested method and the machine suited therefor, crowned tooth flanks can be produced primarily by shaving; the method and the machine, however, are also suited for different precision working methods with two flank meshing engagement, as for example, rolling, honing, etc. The machine in addition offers thereby the advantage that the radial working forces can be absorbed directly by a large-surface guide of the rocking device and only the axial forces must be absorbed by the structural parts which are necessary for the rotary adjustment of the tool head. The arrangement of a rocking device for the inclined positioning of a shaving gear is known from German OS No. 29 12 545. The inclined positioning of the tool, however, does here not occur during the working operation and serves to balance a tilted condition of the workpiece tooth system, such as when the workpiece elastically deforms due to the working pressure applied thereto.
The swivelling movement could be produced with a motor which is arranged on the feed carriage and which drives the rocking device through a worm gear. However, adjustable clearance-free worm drives are, as known, very expensive to make. Aside from this they have, due to the strong friction forces, a poor efficiency and are subject to a quick wear. To transmit the very small swivelling movements which are to be carried out at very specific preselectable points of the feed movement, in the type of machine that is being discussed here, a worm drive is therefore not particularly well suited.
For this reason the machine is provided with an adjusting device for the swivelling drive of the rocking device in the feed carriage. The adjusting device is connected to the rocking device through at least one coupling member and this coupling member is respectively these coupling members are hingedly connected at one end to a rectilinearly adjustable member of the adjusting device and at the other end to the rocking device.
As rectilinearly acting adjusting device, a hydraulic cylinder, having a piston guided therein and a piston rod which is secured thereon and exits from the cylinder, can be utilized when the piston rod is hingedly connected to a coupling member. A more sensitive adjusting of the rocking device is achieved utilizing a threaded spindle and a spindle nut threadedly engaged therewith. The spindle is driven for rotation and is supported in the feed carriage. The spindle nut is connected to the rocking member through the at least one coupling member.
For connecting the coupling member respectively the coupling members to the rocking member and to the spindle nut preferably clearance-free adjustable joints are provided. Especially clearance-free adjustable ball-and-socket joints are very advantageous.
With such a device, the swivelling movement can be transmitted easily and clearance-free. If after a longer operation a clearance begins to occur due to wear, the spindle and the spindle nut, just as with the joints, can be easily readjusted. The coupling member may be a simple coupling rod or a cup or sleeve which partially or entirely surrounds the adjusting mechanism. Of course, two coupling rods which are arranged parallel to one another are also possible. The deviation of the angle of traverse from the path of the rectilinearly adjustable member, which deviation is caused by the change of the inclination of the coupling member relative to the axis defined by the movement of the rectilinearly adjustable member, is negligibly small, if axis and coupling member are arranged approximately tangentially with respect to the circularly shaped guide for the rocking device. "Approximately tangentially" is thereby to be understood as including "parallel to a tangent". In a different arrangement, uneven angles of traverse are achieved by corresponding paths of the rectilinearly adjustable member in the one or in the other direction. The drive for the swivelling movement is explained above and cannot only be manufactured and mounted simply and inexpensively, but operates also clearance-free with low friction and substantially wear-free.